Various types of data storage devices store digital data in magnetic or optical form on a rotating storage medium. Modern magnetic disc drives, for example, comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (“heads”) mounted to a rotary actuator for movement of the heads substantially radially relative to the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The read/write transducer, e.g. a magneto-resistive read/inductive write head, is used to transfer data between a desired track and an external environment.
The heads are mounted via flexures at the ends of a plurality of arms which project radially outward from a substantially cylindrical actuator body. The actuator body, via a bearing assembly, pivots about a shaft mounted to a base deck of the data storage device. The bearing assembly, having a cylindrical hub containing bearings and the shaft, is fitted to and secured within the actuator body. The shaft has a threaded portion extending below the bearing assembly and actuator body and a head, accessible at the top of the bearing assembly, that is adapted to accept a tool such as a screwdriver or wrench. During assembly, the actuator assembly, via the shaft of the bearing assembly is secured to the base deck of the data storage device. That is, the threaded portion of the shaft is screwed into a corresponding hole in the base deck.
Since the heads on the actuator arms are typically maintained in very close proximity to the surface of the storage medium, alignment of the actuator arms should be parallel to the surface of the storage medium. Therefore, it is very important that the shaft of the bearing assembly is properly aligned with the base deck and with the axis of rotation of the spindle motor and the storage medium so that the heads move in a plane parallel with the surfaces of the storage medium. Misalignment of the shaft when securing it to the base deck may cause misalignment of the actuator arms which may in turn cause the heads to contact the surface of the storage medium.
The base deck is machined to ensure proper alignment of the shaft of the bearing assembly. However, the base deck is typically manufactured of a lightweight and relatively soft material such as aluminum. In contrast, the shaft and bearing assembly is typically manufactured of a relatively hard material such as stainless steel. Further, when the shaft is screwed into the base deck significant torsional force can be applied to the mating surfaces of the base deck and shaft. In some cases, these torsional forces cause galling of the softer base deck surface. This galling then causes misalignment of the shaft and actuator assembly.
FIG. 1 is a cross-sectional side view of a prior art bearing assembly for an actuator of a data storage device. The bearing assembly 200 consists of a cylindrical hub 204 in which a shaft 207 is mounted. The cylindrical hub 204 is connected with, and may rotate about, the shaft 207 via bearing 205 and 206 mounted on the inside surface of the cylindrical hub 204 and encompassing the shaft 207.
The cylindrical hub 204 is shaped and sized to mate with a corresponding hole in the actuator body (not shown in this view). The bearing assembly 200 will be pressed into the hole in the actuator body and secured to the actuator via a flange 213 extending from the top of the cylindrical hub 204 and a nut (not shown) engaging threads 214 at the bottom of the cylindrical hub 204.
The bearings 205 and 206 are mounted on the interior of the cylindrical hub 204. Spacer 217 is machined into the interior surface of cylindrical hub 204 and provides for proper positioning of the bearing 205 and 206. Typically, bearings 205 and 206 are adhesively affixed to the interior of the cylindrical hub 204. However, spacer 217 also helps secure the bearings 205 and 206 within the cylindrical hub 204.
The body 208 of shaft 207 passes through the center of the bearings 205 and 206 and is typically adhesively affixed to the bearings 205 and 206. A flange 210 extending from the body 208 of shaft 207 helps to secure the shaft 207 within the bearings 205 and 206 and provides a mounting surface 215 for the bearing assembly 200. Shaft 207 also has a screw 211 extending from the bottom of the shaft 208. Threads 212 on the screw 211 provide a means to attach the bearing assembly to the base deck 102 of the data storage device.
The base deck 102 of the data storage device has a mounting hub 202 extending upwards from its top surface. The mounting hub 202 contains a tapped hole 203 to accept the threads 212 on the shaft 207 of the bearing assembly 200. Additionally, the mounting hub 202 has a machined surface 216 onto which the bearing assembly 200 will be mounted. When assembled, the bearing assembly 200 will be mounted on mounting hub 202 via screw 211 and tightened via a tool such as a screwdriver or wrench applied to an appropriately shaped head 209 on the body 208 of the shaft 207. The shaft 207 is then screwed into the mounting hub 202 until the lower surface 215 of flange 210 makes tight contact with the machined surface 216 of the mounting hub 202.
However, such a design can cause galling of the machined surface of the mounting hub. Since the flange 210 on the lower part of the body 208 of the shaft 207 turns with the body 208 as the screw 211 is tightened into the mounting hub 202, significant torsional force is applied to the machined surface 216 of the mounting hub 202. Additionally, the material of the base deck 102 of the data storage device 100 is likely to be aluminum or a similar lightweight material that is significantly softer than the stainless steel or similar material used for the shaft 207 of the bearing assembly 200. Therefore, galling of the machined surface 216 of the mounting hub 202 may occur. Furthermore, disassembly and reassembly of the drive, such as when the drive is reworked or remanufactured, will only exacerbate the problem by increasing the amount of galling when the bearing assembly is removed and reinstalled.
Accordingly there is a need for a bearing assembly that can be secured to a base deck of a data storage device without galling the surface to which the bearing assembly is secured. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.